1. Technical Field
The present invention generally relates to a developing device used in an image forming apparatus, such as a copier, a printer, a facsimile machine, or a multifunction machine (or a multifunction peripheral) having at least two of coping, printing, facsimile transmission, plotting, and scanning capabilities, and further relates to a process cartridge and an image forming apparatus that include a developing device.
2. Description of the Background Art
Image forming apparatuses typically include a developing device to develop latent images formed on a latent image bearer (e.g., a photoreceptor) with developer, and two-component developer consisting essentially of toner (toner particles) and magnetic carrier (carrier particles) is widely used. The developer bearer has multiple magnetic poles provided thereinside to carry developer on a rotary surface thereof (i.e., sleeve) and supplies toner included in the developer to a development range facing the latent image bearer, thereby developing the latent image formed on the latent image bearer.
There are developing devices that include multiple developer conveyance channels each provided with a developer conveyance member to transport developer in a direction of a rotation shaft (i.e., axial direction) of the developer bearer. While developer is circulated in the developer conveyance channels, a part of the developer is supplied to the surface of the developer bearer. After passing through the development range, developer is collected from the developer bearer and again circulated together with developer existing in the developer conveyance channel. In response to the amount of toner consumed in the development range, toner is supplied through a toner supply inlet to the developing device and mixed with the exiting developer.
In developing devices using two-component developer, typically developer (i.e., initial developer) is contained in the developing device before shipment. If the developer bearer is kept in contact with developer for long time, there is a risk that developer firmly adheres to the developer bearer.
To avoid such an inconvenience, the developer bearer is isolated from the initial developer during transport or storage.
For example, the developing device may be provided with (or shipped with) an easily removable sheet member (e.g., a sealing sheet) to separate the developer bearer from a space (i.e., a developer chamber) containing developer during transport and storage of the developing device, thereby preventing firm adhesion of developer to the developing roller.
An image forming apparatus incorporating the developing device in this state may be shipped. Alternatively, the developing device may be shipped independently as a replacement unit since the operational life thereof is shorter than an apparatus body of the image forming apparatus. The sealing sheet can be incorporated in the developing device also in this state. Users remove the sealing sheet from the image forming apparatus or the developing device as the replacement unit to enable development operation before using the developing device.
For example, JP-4341957-B (JP-2005-189423-A) proposes a sealing sheet bonded to the development casing to seal an opening through which the developer bearer communicates with an interior of the developer conveyance channel serving as a supply channel. In removal of the sealing sheet, the sealing sheet is pulled in a direction parallel to the axial direction of the developer bearer.
There are two-component type developing devices that includes two screws, serving as the developer conveyance members, arranged in parallel to each other, and one of the two screws is disposed facing the developing roller. The screw (i.e., a supply screw) facing the developing roller simultaneously supplies developer to and collects developer from the developing roller. Such a developing device is called a horizontal biaxial circulation-type developing device.
In this developing device, the developer conveyance channel facing the developer bearer is used for supplying developer to the developer bearer and collecting developer from the developer bearer, which is hereinafter referred to as “supply-collection common channel”. After toner therein is consumed in image development, developer returns to the identical developer conveyance channel and again used in image development.
By contrast, there are supply-collection separation type developing devices in which a developer bearer for supplying developer to the developer bearer and a collecting channel for collecting developer therefrom are disposed facing the developer bearer. The supply channel and the collecting channel are separated, at least partly, from each other, and a collecting screw is provided in the collecting channel in addition to the supply screw provided in the supply screw. In this configuration, developer supplied from the supply channel to the developing roller and deprived of toner is not returned to the supply channel but is received in the collecting channel, which is referred to as unidirectional circulation.